The present invention relates to an air bag system for an automotive front passenger seat and, more particularly, to an air bag system which detects a certain level of impact on collision of the automobile and causes a gas to be produced from an inflator that is a gas generator so as to inflate an air bag, thus constraining a passenger seated on the front passenger seat.
One kind of an air bag system for an automotive front passenger seat is a vertical type air bag system comprising an air bag case, an inflator mounted under the bag case, and an air bag mounted above it. In a lateral type air bag system, an inflator is located on one side in an air bag case. An air bag and the inflator are arranged side by side in a direction parallel to the plane of the opening in the air bag case. Various lateral type air bag systems including this kind have been proposed. These proposed systems are discussed in detail below.
One kind of lateral type air bag system has been devised by the present applicant and is described in Japanese Patent Laid-Open No. 191362/1994. This system has an air bag case which opens to a substantially horizontal surface of an automotive instrument panel. An inflator and a zigzag folded air bag are mounted inside the air bag case such that the inflator is positioned ahead of the bag, i.e., the inflator is located closer to the front of the vehicle. An unfolded flat bag portion extends over the inflator. The inflator is provided with gas support ports which are located at a front upper position and a rear lower position, respectively, in a horizontal cross section of the inflator.
In the operation of this air bag system, when a gas is produced from the inflator, the unfolded flat bag portion which is located immediately above the inflator begins to inflate. Therefore, the upper portion of the bag expands upward first and swells into the space defined by the windshield extending obliquely and also by the instrument panel. As a result, the upper portion of the air bag assumes a given shape. Subsequently, the lower portion of the air bag expands. Consequently, the whole bag expands into a desired three-dimensional shape.
An example of a method for folding an air bag is seen in an air bag system described in Japanese Patent Laid-Open No. 227353/1994, also invented by the present applicant. An embodiment of this air bag system is similar in structure to the air bag system described in the above-cited Japanese Patent Laid-Open No. 191362/1994 except that an air bag disposed in a side-by-side relation to an inflator inside an air bag case has an upper, zigzag folded portion adjacent to the inflator and a lower portion which is adjacent to the upper portion and wound into a roll. When the gas is produced from the inflator, the zigzag folded portion loosens more easily than the lower wound portion. By making use of this fact, the upper portion of the air bag expands first when the gas is produced from the inflator. Subsequently, the lower portion expands. As a result, the whole structure swells into a desired three-dimensional shape.
These well-known techniques control the behavior of expansion of an air bag, by taking notice of the structure of a module.
In U.S. Pat. No. 5,405,164 (Japanese Utility Model No. 3014497), a diffuser is located over an inflator with a space between them. This inflator is shaped like a bottle. A gas is ejected from around a port formed at one side of the inflator. This is a so-called hybrid inflator. Since the gas injection portion is distributed unevenly in this way, the diffuser is mounted to regulate the flow of the gas from the port. Specifically, the diffuser is provided with minute holes in positions corresponding to the opening in the inflator. The diameter of the holes increases away from the opening.
Japanese Patent Publication No. 78052/1994 (U.S. Pat. No. 4,998,751) discloses a technique for causing an inflator to exhibit an S-shaped output characteristic curve. In particular, this publication says, "It is an object of the present invention to provide an improved two-chamber expansion system for imparting an S-shaped pressure-time performance curve to an air bag which protects an automotive passenger. In this expansion system, charges of a gas-generating agent in the chambers are simultaneously ignited by a single blasting device. It is a more specific object of the present invention to provide a two-chamber expansion system which delays ignition of the gas-generating agent in the second chamber after the gas-generating agent in the first chamber is ignited, the expansion system being further characterized in that the duration of the delay is achieved by the structure and shape of the blasting device." (column 7, lines 9-17). This system is capable of expanding the air bag slowly at first to mildly push the passenger if he or she is a child assuming an inappropriate posture. Then, a controlled, released gas is supplied into the air bag so as to expand the bag quickly to protect the seated passenger, irrespective of his or her build (column 17, lines 34-38). The output characteristic curve is shaped into an S-shaped form by adopting this inflator. That is, the output of the inflator can be made low at first. However, the effect of the S-shaped characteristic curve may be lessened, depending on the structure of the module located downstream of the inflator as viewed from the injected gas stream. Furthermore, the bag is not expanded mildly throughout the process of expansion.
These air bag systems control the behavior of expansion of airbags, by taking notice of only the inflator output and the regulation provided by the diffuser.